A computer network is a collection of interconnected computing devices that can exchange data and share resources. In a packet-based network, such as the Internet, the computing devices communicate data by dividing the data into small data blocks called packets, which are individually routed across the network from a source device to a destination device. The destination device extracts the data from the packets and assembles the data into its original form. Dividing the data into packets enables the source device to resend only those individual packets that may be lost during transmission.
Routing devices within the network, often referred to as routers, maintain tables of routing information that describe available routes through the network. A “route” can generally be defined as a unit of information that defines a path between two locations on the network. Upon receiving an incoming data packet, the router examines header information within the packet to identify the destination for the packet. Based on the header information, the router accesses the routing table, selects an appropriate route for the packet and forwards the packet accordingly.
The connection between two devices on a network is generally referred to as a link. The link may be a physical transmission line such as a copper wire, a coaxial cable, or any of a host of different fiber optic lines. In addition, the link may be wireless link. As networks grow in size and complexity, devices such as routers and switches can be used to manage and improve data transfer between the various computer devices in the network. Large computer networks, such as the Internet, may include a collection of networks connected by routers that are configured to route data between the networks and computer devices in those networks.
A variety of protocols have been developed to manage and improve data block transfer between the various devices and networks. One class of protocol that has been developed to improve data block transfer is referred to as “multi-link” protocol, in which a sequence of data can be transferred between two devices via more than one link. For example, a subset of the packets can be sent over one link, while the remaining packets in the sequence can be sent over one or more other links. In addition, multi-link protocol may allow a single packet to be transferred over more than one link. For example, the multi-link protocol may break a packet into even smaller data blocks, called fragments, and then send some fragments over one link and other fragments over one or more other links. Multi-link Point to Point Protocol (PPP) (RFC-1990) and Multi-link Frame Relay (FRF.15 and FRF.16) are two current protocols that allow multiple physical links to be treated by a router as a single logical link.
Communicating data blocks such as packets or fragments over multiple links can cause the data blocks to be received in a different sequence than the sequence in which they were transmitted, requiring the data blocks to be “re-sequenced” at the destination device. For example, assume packet A is fragmented into fragments A1, A2, and A3. Packets A1 and A3 may be sent over link1, while A2 is sent over link2. Due to differing propagation delays of link1 and link2, fragments A1 and A3 may be received from link1 before fragment A2 is received from link2.